The present invention relates to a cast resin for optical use, and more particularly to a cast resin excellent in mechanical strength and various optical properties such as transparency and refractive index and thus utilizable in place of glass for various optical elements.
In recent years, a resinous lens is widely used in place of a conventional inorganic glass lens in the field of optical lenses because of its excellent useful properties such as impact-resistant, lightweight, moldable and dyeable properties. Ordinarily known as a material for such resinous lens is, for example, poly(methyl methacrylate), poly(diethylene glycol bis-allyl carbonate), polystyrene and a polycarbonate resin. In case of the poly(methyl methacrylate), and the poly(diethylene glycol bis-allyl carbonate) excellent in impact-resistance, lightweightness and moldability, however, they are so poor in refractive index as to have only about 1.49, and thus need a significant thickness as compared with the inorganic glass when employed as a lens. Accordingly, they are of disadvantage such that they are not suited for the purpose of manufacturing lenses of a high magnification or rendering the weight lighter. In case of the polystyrene and the polycarbonate resin, on the other hand, they have refractive index as high as 1.58-1.59 and are fully satisfactory in this respect. However, they are inherently thermoplastic in nature and thus have drawbacks such that they tend to show optical distortion caused by double refraction at the time of molding such as injection molding and are low in Abbe's number and that they are poor in solvent- and scratch-resistances regarded to be necessary for a substitute for glass lenses and show poor adhesivity to a hard coat film to be applied onto the surface of the lens to improve its surface hardness.
In order to overcome these drawbacks, various technical improvements have hitherto been proposed. In Japanese Laid-Open Patent Appln. No. Sho. 53-7787, for example, there is proposed a resinous glass made of a copolymer of diethyleneglycol bis-allylcarbonate and diallyl isophthalate. In Japanese Laid-open Patent Appln. No. Sho. 59-191708, there is proposed a resinous glass made of a copolymer of a diacrylate or dimethacrylate containing Bisphenol-A and diallyl phthalate with ethyleneglycol bis-allylcarbonate and the like. However, these resinous glasses have some problems in impact-resistance and have such a drawback that control of the reaction in the course of the polymerization is so difficult that the allyl monomers tend to remain unreacted due to difference in the rates of copolymerization, and moreover, the resultant copolymer is poor in weather-resistance.
Further, Japanese Laid-open Patent Applns. Nos. Sho. 62-235901 and 64-45412 disclose a resinous glass made of a copolymer of dibenzyl fumarate with diallyl phthalate, etc. and a resinous glass made of a copolymer of dibenzyl itaconate or dibenzyl mesaconate with diallyl phthalate, etc., respectively. In Japanese Patent Publn. No. Hei 1-60494, there is proposed resinous glass made of a copolymer of a pre-polycondensate of diallyl terephthalate (or isophthalate), methyl acrylate (or methacrylate) and an allyl (or alkyl) mono- or di-carboxylate. However, these resinous glasses involve a problem that they are deteriorated in impact-resistance.
In Japanese Laid-open Patent Appln. No. Sho. 59-140214, there is proposed resinous glass made of a polymer of diethyleneglycol bis-allylcarbonate oligomer. However, the resinous glass involves problems of a low refractive index and coloration of the resin.
In Japanese Laid-open Patent Appln. No. Hei 3-54213, there is also proposed resinous glass made of a copolymer of an oligomer of a diallyl terephthalate series and a monomer of vinyl series. However, this resinous glass is poor in impact-resistance.
Japanese Laid-open Patent Applns. Nos. Sho. 57-28115 and 60-55007 disclose a resinous glass made of a copolymer of a styrene derivative with a heavy metal salt of an unsaturated carboxylate and a resinous glass made of a copolymer of a diallyl phthalate which is nucleus-substituted with a halogen atom or atoms and an allyl benzoate which is nucleus-substituted with a halogen atom or atoms, respectively. These resinous glasses in fact have high refractive indices of 1.58-1.60 but instead lose a merit of lightweight because they contain a large amount of a heavy metal ion and halogen atoms and thus have a heavy specific gravity.
In Japanese Laid-open Patent Appln. No. Sho. 55-13747, there is proposed a resinous glass made of a copolymer of an acrylic or methacrylic monomer containing Bis-phenol A, a monomer of styrene series and an aryl methacrylate monomer, etc. However, this resinous glass involves a problem that it incurs coloration of the resultant lens and is poor in impact-resistance and adhesivity to a hard coating film.
In Japanese Laid-open Patent Appln. No. Sho. 59-133211, there is proposed a resinous glass of a copolymer of a hydroxy diacrylate or dimethacrylate containing an aromatic ring, a monomer of diisocyanate and a monomer of styrene series. However, an apparent merit of this resinous glass residing in a high refractive index of around 1.60 is compensated with an incidental demerit of low weather-resistance and a high specific gravity. Furthermore, in Japanese Laid-open Patent Appln. No. Hei. 3-70715, there is proposed a resinous glass with excellent transparency and a high refractive index obtained by thermocuring a composition comprised of a methacrylic ester, a polyfunctional methacrylate and a diacrylic diester and incorporated with a peroxy ester as a curing agent. However, this resinous glass has such a drawback that it is poor in adhesivity to a hard coating film and has an impermissibly great specific gravity.
Under the above circumstances, there is a great demand in the field of synthetic resins for use in optical elements to develop a new type resin which is excellent in various physicochemical properties such as transparency, mechanical strength, solvent-resistance and weather-resistance, and thus overcomes all the drawbacks as seen in the conventional resins.